Interpretive Summary: Insect neuropeptides are short chains of amino acids (the building blocks of proteins) that regulate a number of physiological processes critical for insect survival. For example, members of the "insect kinin" class of insect neuropeptides regulate water and mineral balance as well as digestive processes in a number of insects. Nevertheless, insect neuropeptides in and of themselves hold little promise as insect control agents because of their susceptibility to being degraded in the target insect, instability under environmental conditions, and inability to pass through the outside skin (cuticle) of the insect. In this paper, we report on the development of insect kinin mimics that are resistant to the processes insects normally use to degrade neuropeptides. These mimics are even more active than the natural neuropeptides in affecting the ability of the insect to maintain water balance. This work leads us one step closer to the development of practical neuropeptide-like chemicals that will be effective in controlling certain pest insects but will be very environmentally friendly.

Technical Abstract:
Analogs of the insect kinin family containing a sterically hindered aminoisobutyric acid (Aib) component prove to be resistant to hydrolysis by housefly (Musca domestica) angiotensin converting enzyme (AnCE), an endopeptidase capable of hydrolysis and inactivation of the naturally occurring insect kinin peptides. The Aib residue is compatable with formation of a turn in the active core region that is important for the biological activity of the insect kinins. One of the Aib-containing analogs is eight fold more active than the most active endogenous insect kinin in a cricket (Acheta domesticus) Malpighian tubule fluid secretion assay. As the analog is blocked at both the amino and carboxyl termini and is resistant to an endopeptidase present in insects, it is better adapted than the endogenous peptides to survive for long periods in the haemolymph. Enzyme-resistant insect kinin analogs can provide useful tools to insect researchers studying the neuroendocrine control of water and ion balance and the physiological consequences of challenging insects with diuretic factors that demonstrate enhanced resistance to peptidase attack. If these analogs, whether in isolation of in combination with other factors, can disrupt the water and/or ion balance, they hold potential utility for the control of pest insect populations in the future.